Call set-up is a standard procedure performed in a mobile communication network. The set-up procedure is initiated upon connection request of a terminal (originating terminal TO), such as a mobile phone or any other type of mobile communication device, which generally connects via a radio access network. A controller of the radio access network, such as a radio network controller (RNC) of UTRAN (UMTS Terrestrial Radio Access Network) or a base station controller (BSC) of a 2G radio access network (RAN), exchanges signalling traffic with an access gateway, such as a mobile switching center (MSC) of a core network. This so-called originating access gateway (O-AGW) sends connection set-up signalling through the core network to a terminating access gateway (T-AGW), which communicates with the terminating terminal (Tt) through a terminating radio access network. The signalling path (also called call routing path) from the O-AGW to the T-AGW which runs on the so-called signalling plane can pass through further nodes of the core network, in particular control nodes controlling media gateways, such as further MSCs or the like. The nodes of the core network through which the signalling path runs control media gateways, by means of which a media path is established on the media plane, also called user plane, through the core network. The media path further extends from the MGW of the O-AGW and the T-AGW through the respective radio access networks to the originating terminal and the terminating terminal, respectively.
The signalling plane established by means of the access gateways and the control nodes transports signalling traffic, while the media plane established by means of the media gateways transports media contents, such as voice data, video data or other types of user data. There are several methods of setting up a connection upon receiving a request from a terminal, one of which is described in detail further below with respect to FIG. 6. In general, the O-AGW sends a set-up message to the T-AGW, with the control nodes in the signalling (or routing) path instructing their associated media gateways (MGWs) to establish at least part of the media path.
After receiving the set-up message and exchanging signalling traffic with the terminating terminal, the T-AGW sends a response message to the O-AGW for finalizing the set-up of the media path, over which a ring back tone may be transmitted.
The media path generally comprises a forward channel (or “A-Channel”), which transports media contents in a direction from the MGW of the originating AGW to the MGW of the terminating AGW, said direction also being called downstream. The backward channel (also called “B-Channel”) transports media contents from the MGW of the terminating AGW to the MGW of the originating AGW, said direction also being called upstream. Downstream may also be defined as the direction of transmission of a connection set-up message and upstream as the direction of transmission of the response message. Note that in the art, the terms upstream and downstream are not always used in the same manner. The particular meaning may need to be derived from the context in which the terms are used. As an example, downstream with respect to the B-channel may correspond to the above mentioned upstream direction, as contents is transported in backward direction on the B-channel.
The terms downstream and upstream may also be used to define a relative position of a node in the signalling or the media path. As seen from a node in the path, an upstream node can be a node preceding said node in the path and a downstream node can be a node succeeding a node in the path with respect to the direction of transmission of a particular message or contents. In such a context, an upstream (or downstream) node may be different when seen from the A-channel or the B-channel.
In some networks, the core network nodes establish the forward channel upon receiving the set-up message and the backward channel upon receiving the response message. In other networks, the nodes of the core network establish both channels upon receiving the set-up message, with the receiver addresses of the media gateways being exchanged between the control nodes by means of inter-node signalling (so called “Fast Track”).
In other scenarios, such as roaming terminals, the media and signalling path can be more complex. As an example, further core networks, transit networks and the like may need to be traversed to reach the core network of a particular operator. The radio access network of the originating terminal may for example connect to an originating core network, and further via one or several transit networks to the core network of the operator. A network through which the core network is accessed may be termed access network. It may thus be a RAN, another core network, or the like.
In conventional network architectures, the media path is established through the radio access network and possibly further access networks and the core network at call set-up and kept over the duration of the call. Any node in the media path has access to the media plane, it can for example read data from the media plane (e.g. for multi-party conferences or for call storage) and it can write or insert data into the media plane (e.g. for multi-party conferences or announcements). Such supplementary services generally reside within the core network and can take advantage of such simple media plane access.
In some countries and networks, the number of voice calls that originate and terminate within one area (e.g. city or region, also termed local calls) can be relatively high. Two terminals may even reside within one radio cell. In terms of connection costs, linking to such a cell is rather expensive, it may occur e.g. by microwave links or even via satellite.
In order to reduce the connection costs, it is desirable to identify such calls and to provide a short-cut of the media path within the radio cell or radio access network, without using the whole media path through the core network. Such a shortcut of the media path may be termed “local call local switch (LCLS)”. Users may benefit from providing such shortcuts as the more direct routing of the media contents may provide a higher voice quality and a lower speech path delay, while at the same time, the operator of the network may benefit from the reduced operation expenditure. A shortcut of the media path may also be termed “local shortcut”.
With respect to a local shortcut, the problem arises that some of the nodes in the signalling path may require access to the media plane. If such a shortcut is switched, then core network nodes may no longer be capable of accessing the media contents, i.e. read or write to the media plane. When setting up the connection, it is often not clear which supplementary services need to be provided by the nodes in the signalling path. Services, such as lawful interception, recording services in the home network, tone insertion and announcements generally required media plane access, preventing local shortcuts. It is thus desirable to improve the end-user experience, such as distortion delay etc., and reduce the operator expenditure, such as the required resource capacity and link capacity, by improving the switching of local shortcuts. In particular, the number of situations, in which local shortcuts can be switched, should be increased. It is desirable to determine the situation in which a local shortcut can be established. Furthermore, it is desirable to determine the access needs or requirements to the media plane of the nodes in the signalling path.
It is thus an object of the present invention to obviate at least some of the above disadvantages and to improve the setting up of connections in a mobile communication network.